System of pulverizing, feeding, and transporting of material



July 1, 3946. J. L A Y 2,403,976

SYSTEM OF PULVERIZING, FEEDING, AND TRANSPORTING OF MATERIAL Filed May22,.1943

INVENTOR.

JamesL Harvey ATTORNEY Patented July 16, 1946 UNITED STATES PATENTOFFICE SYSTEM OF PULVERIZING, FEEDING, AND TRANSPORTING OF MATERIALApplication May 22, 1943, Serial No. 488,013

12 Claims. 1

The invention disclosed herein pertains to a system providing for thepulverization of a solid material capable of being transported in afinely divided state by means of a current of air or other gaseousmedium. The material may suitably be a fuel such as coal, although otherfuels, or other materials of a non-combustible character, are equallywithin the scope of the invention. The invention further contemplatestransportation of the pulverized product to one or more points of use.

A specific application of the invention is to an air-swept pulverizingand distributing system wherein a current of air or other gaseous mediumis maintained throughout the system for removing pulverized fuel from apulverizer and for transporting the pulverized fuel direct to one ormore burners in the manner commonly referred to as direct-firing.Nevertheless certain features of the invention may be found useful inother known systems employing such additional apparatus as cyclones,storage bins, and feeders incident to the transportation of thepulverized material from the pulverizer to the ultimate point of use. r

In a direct-fired system employing a plurality of burners in one or morefurnaces, it may often be found desirable to utilize a single pulverizerfor supplying the entire fuel requirements of several burners operatingsimultaneously. Where a number of small furnaces are involved, it mayalso be found both convenient and economical to distribute fuel to theburners of several furnaces from a single continuous main conduit systemhaving both ends connected to the pulverizer to provide a closedcirculating path or circuit for the fluent. fuel mixture; individualburners being supplied through individual branch lines connected to theconduit at intervals along its length, and any surplus quantity of themixture above that required by the burner or burners in operation beingreturned in whole orin part to the pulverizer or other advance point inthe system for recycling,

If one or more burners should be operated at varying capacities, or ifthe cycles of operation of individual burners should be different, theresulting changes in overall fuel consumption make it necessary toprovide suitable adjustment of the rate at which material is fed to thepulverizer. Such conditions may be found in metallurgical plants, forexample, where a different number of furnaces for the same or diiierentprocesses may be in operation over different periods, thus causingabrupt and Wide variations in fuel consumption for which there must beadequate control of pulverizer operation to suit each new condition.

In the usual direct-fired system where the entire output of thepulverizer is utilized and none of the mixture is returned forrecycling, it has been found that the quantity of pulverized coaldischarged from the pulverizer is substantially proportional to the rateof flow of primary air therethrough so long as a proportional amount ofcoal is maintained therein. This characteristic of air-swept pulverizeroperation is utilized in U. S. Patent 1,965,643 to R. M. Hardgrovewhereby the feed of material to the pulverizer is controlled to maintaina certain level or reserve quantity of material in the pulverizer forthe existing rate of flow of primary air.

According to the present invention, an airswept pulverizer and transportsystem is proposed wherein any desired proportion of the pulverizeroutput may be withdrawn, and any remaining proportion circulated bybeing returned to the pulverizer, or in part to the pulverizer and inpart to some other point in the system in advance of a point ofwithdrawal, the proportions of the mixture so withdrawn and returnedbeing varied as desired for a given value of pulverizer output, or fordifferent values.

As an accompaniment to such an objective, it is proposed to maintainunder all conditions a proper relation between fuel and air in themixture available for withdrawal.

An additional object concerns the supply of raw material to the systemand the maintenance of a proper reserve of material in the process ofpulverization within the pulverizer, each in relation to varying demandson the System.

Another object contemplates controlling the rate at which raw materialis fed to the pulverizer in accordance with fluid flow conditions withinthe system, including for example, the rate at which a portion of thepulverizer output is returned for recycling.

A further object is to correlate indications of fluid pressureconditions existing at different points in the systemfor the purpose ofcontrolling pulverizer operation.

These and other related objects of the invention may be achieved in themanner about to be described, an arrangement of apparatus suitable forthe purposes of the invention being diagrammatically indicated in theaccompanying drawmg.

In the drawing, an air-swept pulverizer I0 is shown with its associatedfeeder I2 by which raw unpulverized material such as coal, is fed to thepulverizer from a suitable bin 14 or other source of supply, the feederbeing driven by a multispeed electric motor l6, for example, as a meansof providing different rates of feed.

Air or other gaseous medium to provide a carrier for the pulverizedmaterial is admitted to the pulverizer through an inlet duct M3 by whichthe carrier medium at an elevated temperature is supplied from a sourcenot shown, a branch inlet 20 conveniently open to the atmosphereproviding a means for admitting tempering air to the duct I8; regulatingdampers 22 and 2:1 being suitably provided in the respective inletconnections for maintaining the temperature of the carrier mediumentering the pulverizer at a desired predetermined value.

A fan 26 connected to the pulverizer outlet by the discharge duct 28induces a draft through the pulverizer which causes the carrier air topass into the pulverizer from the duct 18 and to pass through thepulverizer where it picks up the pinverized material to provide a fluentmixture, which for the purpose of this example may consist of pulverizedfuel suspended in a stream of primary combustion air, the term air beingused generally whether or not a portion of the carrier medium isobtained, as is sometimes the case, from a source of hot flue gases. Themixture is discharged from the pulverizer through the duct 28 as afluent stream, passing through the fan 26 and into the fuel main 39 fromwhich it is delivered to one or more points of use.

The illustrated embodiment provides for delivery of the pulverulent fuelmixture to a plurality of burners 32, 3'4, 36 and 38 associated with aplurality of furnaces 4%, t2 and i l, each burner line 43 preferablybeing fitted with a plug valve dfl adjacent its connection to the fuelmain to, and with a second valve 58 of the butterfly type intermediatethe plug valve and the burner. The plug valves are for the purpose ofcutting off and completely isolating the supply of fuel from individualburners so that any number of burners maybe operated, as desired, whilethe butterfly valves serve as a means'for regulating the flow of fuel tosuch burners as are in operation. In practice, the fuel main 333 may beso arranged that the .greater part of its length is horizontallydisposed and at a level higher than the level at which the burners arelocated, thus enabling the burner lines 56 to be conveniently connectedto the under side of the fuel main 3!] and to extend verticall downwardtherefrom for connection to individual burners. A secondary supply ofair may be admitted to the burners or to the furnaces for combustionpurposes, but the details of such secondary supply do not enter into thesubject of the present invention and are therefore omitted from thedrawing.

The fuel main 3.9 is continued beyond the last burner to be served, hereindicated as burner 38 for furnace 34, to provide a conduit length 52for returning to the pulverizer any surplus quantity of the fuel-airmixture which is not delivered to the-burners, the return length 52, asshown, being connected to the pulverizer ill at a location opposite toth location at which the primary air is admitted through duct l8, and ata somewhat higher level. There is thus provided a single continuous mainconduit system consisting of the .disohargeduct 28, fan and fuel main 38including its return length 52, having both ends connected to thepulverizer iii and thereby forming a closed path or circuit over whichat least a portion of the mixture initially discharged from thepulverizer maybe circulated. The fuel main may be formed of differentsizes of conduit with reductions in cross section at intervals as at 56,56 and 58 to maintain a sumciently high velocity of fluid flowthroughout to prevent fuel from settling out of the flowing mixture.

The pulverizer shown is of a known type utilizing a circular series ofsteel balls 63 operating between a stationary lower grinding ring '52and a revolving upper grinding ring 64, the latter 4 being operativelyconnected to the rotating spindle -56 to which an extension casting {i8is fitted to provide an annular passage or throat 18 for directing thecarrier air into the grinding zone. A duct 12, formed in the base of thepulverizer and open at its upper side to the throat 10, provides amixing chamber for fresh incoming primary air entering at one end frominlet duct i8 and for the surplus fuel-air mixture entering at alocation adjacent its opposite end from the return line 52. Theintroduction of the surplus mixture at the level indicated takesadvantage of the conical formation of the pulverizer casing as at Mwhich serves to deflect the returning,

mixture downwardly into the duct 12 and obliquely against its bottomwall, thus producing a degree of agitation which tends to promote aredistribution of the fuel particles within the chamber and a morethorough mingling of the two streams to provide a relatively homogeneoustotal mixture of fuel and primary air for admission through the annularthroat It.

It is evident that in the operation of a directfired circulating systemsuch as has been described, there can be wide variations in fuelconsumption due to the ability to operate a different number of burnersat different times, and, if necessary, to operate individual burners atvarying capacities. The resulting variations in fuel consumption imposevarying demands on the pulverizer unit so that it becomes necessary toincrease or decrease the rate at which raw coal is fed to thepulverizer, such changes in load requiring a change in the rate of fuelinput which while satisfying the demand for a dilferent output ofpulverized fuel will also maintain the proper level or reserve ofmaterial in the pulverizer for the particular load involved; the levelof material being preferably increased as the load is increased anddecreased as the load is decreased.

Since the pulverized fuel is maintained throughout the system in afluent state, that is, in suspension in a current of primary air orother gaseous carrier medium, an indication may be obtained of the rateof flow of the fluent fuel mixture through a given portion of the systemby measuring the pressure differential across that particular portion. Asimilar measure may be obtained of the rate at which air is supplied tothe system. These are factors which enter into the control of pulverizeroperation in the present system.

Referring again to the drawing, a measure of air flow to the pulverizeris conveniently obtained by employing an orifice 16 in the inlet ductl8, the resulting differential pressure across the orifice beingtransmitted by tubes 18 and 8D to the pressure sensitive diaphragm 82suitably mounted for movement within a stationary casing 84. Thepressure differential resulting from the flow of air and coal insuspension through a selected portion of the pulverizer, includingparticularly the grinding zone thereof, is transmitted by tubes 86 and88 to the pressure sensitive diaphragm 9!] within the casing 92, thetube 86 being connected to a pressure point in advance of the grindingzone, for convenience to the downstream side of the orifice 16 as in thecase of tube 86 for diaphragm 82, and tube 88 being connected to apressure point following the grinding zone, for convenience to a pointadjacent the pulverizer outlet. The rate at which surplus fuel and airare returned to the pulverizer under varying conditions is measured interms of the pressure differential across a selected ortion of thereturn conduit 52, tubes 94 and 06 being connected to the conduit atrelatively widely separated locations and the existing pressuredifferential transmitted thereby to the pressure sensitive diaphragm 98within the casing I 00.

The relative pressures acting upon diaphragm 82, 90 and 98 arecoordinately utilized to effect movement of the lever I02 which ispivoted about a point I04 fixed in relation to the casing 84 at oneside. The lever I02 carries a contactor element I05 whereby uponmovement of the lever I02 abouts it pivot point I04 certain electricalcircuits to be later described are selectively energized to control theoperation of the feeder motor I ii and thereby the rate at which coal isfed to the pulverizer.

The force exerted by diaphragm 82 is transmitted to the lever I02 bymeans of a pin I03 movable with the diaphragm 82 and extending throughopposite walls of the casing 84, one end of the pin engaging the leverI02 at a predetermined distance from. the fulcrum point I04, Theopposite end of pin I00 engages a second pivoted lever IIO also at apredetermined distance from a fixed fulcrum point II2, the lever armdistances in both instances being suitably equal as shown.

The force exerted by diaphragm 99 is applied to the lever I02 by meansof a pin II4 extending through a side wall of casing 92, and similarly,the force exerted by diaphragm 98 is applied to the lever IIO by meansof a pin 'IIB extending through a side wall of easing 60. The

casings 92 and I00 preferably have adjustable mountings as at H8 andI20, whereby their position may be varied relative to the respectivefulcrum points I04 and H2, to thus increase or decrease the lever armdistances at which the forces exerted by diaphragms 90 and '98 areapplied to the respective levers I02 and H0.

Springs I22 and I24 are provided to apply an initial loading to thelevers I02 and H0 respectively, each spring having an adjustment I26 bywhich a desired degree of tension or compression may be obtained.

It may be assumed that the burners shown are of such capacities thatwhen all are operating simultaneously at full ratings the total deliveryoffuel and air tothe burners is practically equal to the total output offuel and air from the pulverizer, in which case there is a minimum ofsurplus fuel and air being returned to the pulverizer and thedifferential pressure transmitted through tubes 04 and 90 approacheszero. Under such conditions, virtually clean air alone is admittedthrough the pulverizer throat and, in accordance with knowncharacteristics of airswept pulverizer operation, the differentialpressure across the clean air orifice l6, as transmitted .through tubesI8, 80 to diaphragm 82, bears a definite relation to the difierentialpressure across the pulverizer I0, as transmitted through tubes 86, 88to diaphragm 00; this relation being determined by the pulverizer designand the grindability, sizing, and moisture content of the fuel beinghandled. As long as the fuel characteristics remain the same, and airflow through the pulverizer is kept constant, the pressure differentia1across the pulverizer cannot be increased or decreased without anaccompanying increase or decrease of the pulverizer output; andconversely, the pulverizer output cannot be increased or decreasedwithout an accompanying increase or decrease of the pressuredifferential across the pulverizer.

Therefore, with return flow through conduit 52 practically zero, theentire control of pulverizer operation is subject to the relative forcesexerted by diaphragms 82 and on lever I02, whereby motor IE will beoperated at intervals at the proper speeds to provide a fuel-air mixtureof a predetermined fuel-air ratio at the required pul verizer output;the term fuel-air ratio being defined as the cubic feet of air atpulverizer outlet temperature per pound of fuel.

When the opposing forces exerted on lever I02 by the diaphragms 82 and90 are balanced, the contactor I06 is held clear of all upper and lowercontacts I48, I42, I44 and I46, and feeder I2 is operated tov feedmaterial to the pulverizer at a predetermined low rate. If the level orreserve quantity of material within the pulverizer should decrease,,thus decreasing differential pressure across the pulverizer, the forceexerted by diaphragm 02 overcomes the force exerted by diae phragm 90,and lever I02 is moved counterclockwise to cause contactor I06 tosuccessively con tact the upper contacts I40 and I42, and feeder I2 isoperated to feed material to the pulverizer at a predetermined high.rate to restore th normal operating level for the required rate ofpulverizer output. If the level or reserve quantity of material withinthe pulverizer should increase beyond the normal operating level, thedifferential pressure across the pulverizer is correspondinglyincreased, and the force exerted by diaphragm 90 overcomes the forceexerted by diaphragm B2, and lever W2 is moved clockwise to causecontactor W5 to successively contact the lower contacts I44 and MB, andoperation of feeder i2 ceases.

When operation of the system is such that an appreciable fiow of thepulverized material and air mixture occurs in the returnline 52, thedensity of the fluid admitted through the pulverizer throat I0 isincreased and the same relation of pulverizer differential to fresh airdifferential no longer holds. Furthermore the new relation may besubject to variations due to the varying rates at which the mixture isreturned, and to the relation Which the proportion of the mixturereturned bears to the total pulverizer output for a given load.

Assuming one of the burners, burner 32 for example, to be shut off, theproportion of the total pulverizer output formerly delivered to thatburner becomes a surplus proportion of the total mixture which isreturned through conduit 52 to the pulverizer I0 where it is mingledwith the fresh air entering through inlet I8 for combined flow throughthe pulverizer throat 10, the resultant modified mixture constituting ineffect a modified carrier medium of increased density. Tests haveindicated that when an appreciable proportion of the mixture is returnedto the pulverizer, as through the conduit 52, the relation between thedifferential pressure across the pulverizer and the differentialpressure across the clean air orifice I6 is modified, as compared withthe relation for zero return flow, and that the relative response of thetwo diaphragms 82 and 90 is also modified.

In order to compensate for the effect which return flow has on thefunctioning of diaphragms 82 and 90, the third diaphragm 98 is maderesponsive to fluid flow conditions in the return line 52, as indicatedby differential pressures transmitted through tubes 94, 96, thediaphragm 98 acting to oppose the operation of diaphragm 90 and toassist the operation of diaphragm 82; the force exerted by diaphragm 98being applied to lever H and transmitted through pin I08 to lever I02,so that the operation of diaphragm 98 is superimposed on the operationof diaphragms B2 and 90 which normally act to control the supply of rawmaterial in relation to fresh air to maintain a fuel-air ratio ofconstant value, or of a predetermined range of values, throughout theentire range of pulverizer output capacities. Based on the knownpulverizer characteristics as heretofore mentioned, such predeterminedvalues of fuel-air ratios may be Obtained by suitable adjustment of theposition of diaphragm 60 relative to the fulcrum I04, and by suitableadjustment of the spring I22; the diaphragm adjustment being made formaintaining either a constant or varying fuel-air ratio throughout agiven range of pulverizer capacities, and the sprin adjustmenttransposing the value of fuel-air ratio by the same amount for allcapacities within thegiven range. The combination of these two simpleadjustments provides a means for securing the desired value or values offuel-air ratio for the particular arrangement of burners. The return ofa proportion of the outgoing mixture to the pu1- verizer adds to theamount of pulverized material and air flowing through the pulverizer,and accordingly tends to increase the differential pressure across thepulverizer, thereby modifying the normally fixed relation between thedifferential pressure across the mill I0 and the difierential pressureacross the air inlet'orifice 15. The diaphragm 98 acting in oppositionto the pulverizer differential diaphragm 96 serves to cancel out thatcomponent of the pressure drop through the pulverizer which is due tothe returned pulverized material and air, and enables the operation offeeder I2 to be kept in step with the incoming fresh air as in the casewhere none of the mixture is circulated and, in consequence, fluid fiowthrough the return line 52 is zero. The differential pressuretransmitted through tubes 94 and 98 to the diaphragm 58 need not be ofany specific value since a compensating adjustment may be made as at Ito suitably position the diaphragm relative to the fulcrum I I 2 forlever I It.

Any number of burners may be cut in or out as desired, and in accordancewith operations reported to date, varying loads may be carried withthecontrol apparatus functioning satisfactcrily throughout a range ashigh as 8:1 in. pulverizer capacities.

The manner in which movement of the lever I 02 is correlated tooperation of the feeder motor I5 will be understood from the wiringdiagram which by way of example is based on a source of three-phasealternating current supply for operation of an electric motor havingseparate windingsfor different speeds. A transformer I28 suitablyconnected to the main supply lines AC provides reduced voltage at itssecondary terminals I38 and I32 for the several control circuits, thesecondary terminal I being connected by lead I34 to the arm I36 of aselector switch I38,

the switch arm I being shown in the off position.

Four adjustably fixed contacts I40, I42, I44 and I43 are shown arrangedin pairs at opposite sides of the movable contactor element I06, thecontacts I48 and I44 being adjusted to points nearer to the contactorI06 than the contacts I42 and I46, and the contactor I 05 being madeflexible so that movement of the lever I62 in one direction causescontact to be made first with contact I40, and then additionally withcontact I42. Movement of lever I82 inv the opposite direction causescontact to be made first with contact I44 and then additionally withcontact I46. Lead I48 connects the contactor I08 with a contact I58 atthe automatic position of switch I38.

, Upper contact I42 is connected to one terminal of the relay coil I52by lead I54, while upper contact I40 is connected to the same terminalthrough the normally-open relay switch I56. The other terminal of relaycoil I52 is connected to terminal I32 of the transformer secondary bymeans of lead I58 which serves as the common transformer returnconnection for the various relay coils shown.

Lower contact I46 is connected to one terminal of the relay coil I60 bylead I62, while lower contact I 44 is connected to the same terminalthrough the normally-openrelay switch I64 Theother terminal of relaycoil Ififl'is connected to terminal I32 of the transformer secondarythrough the commonconnection I58.

A second contact I66 at the automatic position of the selector switchI33 is connected by lead I68 to one side of the normally-closed relayswitch I10, the other side of which is connected through thenormally-open relay switch Hi2 to one terminal of relay coil I14, andthrough the normally-closed relay switch I16 to one terminal of relaycoil I18. The other terminals of relay coils I14 and I18 are connectedto terminal I32 of the transformer secondary through the common returnI58.

Switches I88 and I82 are three-pole switches, operated respectively bythe relay coils I14 and H8, for establishing connections between themain power supply lines AC and the high and low speed windings of thefeeder motor I6; a three-wire connection I84 leading from switch I tothe high speed winding, and a three-wire connection I86 leading fromswitch I82 to the low speed winding.

When the selector switch I38 is set for autov matic operation the motorI6 will operate at low speed as long as contactor I06 is held clear ofall contacts I40, I42, I44 and I46. Under such conditions, the relaycoil I18 is alone energized, whereby the associated switch I82 is heldclosed, and ,power is supplied only through connection I86 to the lowspeed winding of the motor; the control circuit extending from thetransformer terminal I30, through lead I34, switch arm I36, switchcontact I66, lead I68, normally-closed relay switches I10, I16, relaycoil I18, and return connection I58 to the transformer terminal I32.

Counterclockwise movement of the lever I02 causing contactor I05 tocontact upper contact I 40 results in the control circuit voltage beingapplied to one side of the normally-open relay switch I56. Whencontactor I85 is brought into contact with upper contact I42, there is acircuit established through the relay coil I52 whereby the associatedrelay switches I5 I12 and I16 are actuated, and the motor I6 caused torun at high speed. The control circuit in this case is from thetransformer terminal I30, through lead I34, switch arm I36, switchcontact I36, lead I68, normally-closed relay switch I10, throughnormally-open relay switch I12 now closed, relay coil I14, and returnconnection I58 to the transformer terminal I32. The opening of switchI16 opens the circuit through relay coil II'8'to interrupt the powersupply to the low speed winding, while the closing of switch I12completes the circuit ,9 through relay coil I14 to close switch I80 andthereby transfer the power sup-ply to the high speed winding. The motorwill continue to operate at high speed. as long as contactor I06 remainsin contact with upper contact I40, whether or not contact is broken withupper contact I42.

Clockwise movement of lever I02 results in similar successive contactingof lower contact points I44 and I46 by contactor I06. When contact imade with point I46 the power supply to the motor I5 is cut off and themotor stops, the contact with point I46 causing relay coil I60 to beenergized and the associated relay switches I64 and I I0 to be actuated;the opening of normally-closed switch I interrupting the control circuitthrough transformer I28 so that neither relay coil I14 nor I18 isenergized and both power switches I80 and I82 remain open.

Additional contacts I88 and I90 may be provided on the selector switchI38 if it is desired to include manual control of motor operation. Forthis purpose, a connection may be made from contact I88 direct to pointI92 of the circuit, and another from contact I90 direct to point I94,whereby lowspeed or high speed operation may be obtained by moving theswitch arm I36 either to contact I88 or to contact I90.

Certain features disclosed herein are also disclosed and claimed in mycopending application, Serial No. 531,776, filed April 19, 1944.

The invention as herein disclosed in accordance with the provisions ofthe statutes will be understood by persons skilled in the art to beapplicable in arrangements other than those specifically described, andto include features which may be used to advantage without acorresponding use of other features, within the scope of the appendedclaims.

I claim:

1. In combination with a pulverizer having an annular grinding zone in alower portion thereof wherein a reserve of material in the process ofpulverization is maintained during normal operation, said pulverizerhaving an outlet at the upper side of said grinding zone, means forfeeding material to be pulverized into said pulverizer above saidgrinding zone, means forming an an nular throat passage marginally ofsaid grinding zone, means for maintaining an upward current of airthrough said annular throat passage for discharging through said outleta fluent mixture comprising pulverized material suspended in said air, amain conduit having one end connected to said outlet and having itsopposite end open to the interior of said pulverizer at the lower sideof said grinding zone, mean for withdrawing from said conduit varyingproportions of said pulverizer output mixture, said conduit constitutinga conductor for returning a remaining proportion of said mixture to saidpulverizer at a density substantially equal to the densityof the totalmixture initially discharged, means separate from said conduit foradmitting said air to said pulverizer, means for causing said returnedproportion of said mixture to become mingled with said air at a locationaxially below and adjacent said annular throat passage for combinedupward flow through said pulverizer, and means for regulating saidmaterial feeding means comprising pressure sensitive means responsivesimultaneously to pressure differentials indicative respectively of saidair admission to said pulverizer and of said combined fluid flow througha predetermined portion of said pulverizer inclusive of said annularthroat passage.

2. In a system of theclass'described, an airswept pulverizer having anannular grinding zone within the lower portion thereof in which materialin the process of pulverization is maintained during normal operation,said pulverizer having an outlet from its upper portion fordischarging afluent mixture comprising pulverized material suspended in air, meansfor withdrawing from said system varying amounts of" the total mixturedischarged from said pulverizer outlet, means for supplying air tosaidpulverizer at a level below said grinding zone, means"sep arate fromsaid air supplying means for returning to said pulverizer a remainingportion of said mixture at a density substantially equal to the densityof the. total mixture initially discharged. means for mingling thereturned portion of said mixture with said supplied air, means fordirecting said returned portion mingled with said supplied air upwardlythrough said pulverizer inclusive of said grinding zone, means forfeeding material to be pulverized into said pulverize'r above saidgrinding zone, means for regulating said feeding means comprisingpressure sensitive means responsive to a pressure differentialindicative of said mingled fluid flow through said pulverizer inclusiveof said grinding zone, and means for rendering said regulating meansoperative in accordance with a measure of the .return flow of saidremaining mixture portion.

3. In combination with an air-swept pulverizer arranged to discharge afluent mixture of pulverized material and air, means for feeding material to be pulverized to said pulverizer, means for returning aportion of said mixture to said pulverizer,.means for regulating therate at which said material to be pulverized is fed to said pul verizer,and means responsive to the flow of said portion being returned forcontrollingtheloper;

ation of said last named means to maintain a predetermined ratio of airto material in said mixture.

4. In combination with an air-swept pulverizer arranged to discharge afluent mixture of'pulverized material and air, means for feedingmaterial to be pulverized to said pulverizer at varying rates to providevarying output capacities,

mean for returning'a portion of said mixture to said pulverizer, meansfor regulating the rate at which said material to be pulverized is fedto said pulverizer, and means responsive to the flow of said portionbeing returnedffor' controlling the operation. of said last named meansto main tain the ratio of air to material in said mixture substantiallyconstant at said varying output capacities of said pulverizer.

5. In combination with an airswept pulver izer arranged to discharge afluent mixture of pulverized material and air, means for feedingmaterial to be pulverized to said pulverizer, means for delivering aportion of said mixture to a point of use, mean for returning the remainder of said mixture to said pulverizer, means for measuring the rate atwhich said remainder is returned to said pulverizer, and meanscontrolled by said last named means for regulating the operation. ofsaid feeding means. I

6. In a continuous conduit system including a pulverizer, means forsupplying material to be pulverized ,to said pulverizen'mean forsupplying carrier air to said pulverizer for transporting pulverizedmaterial therefrom and through said system, means for withdrawing aportion of said pulverized material and air from a part of said systemother than said pulverizer, means for maintaining another portion ofsaid pulverized material and air in circulation throughout said system,means for regulating the rate at which said material to be pulverized issupplied to said pulverizer, and means responsive to the rate ofcirculation of said other portion of pulverized material and air forcontrolling the operation of said regulating means.

7. In combination with an air-swept pulverizer having separate inletsfor fuel and air and having an outlet for pulverized fuel mingled withsaid air, a continuous conduit having one end connected to saidpulverizer outlet and its opposite end connected to said inlet for air,means for supplying fuel to said pulverizer, means for withdrawing aportion of said fuel-air mixture from said conduit, means for measuringthe rate at which the remaining portion of said mixture is returned tosaid pulverizer air inlet through said opposite conduit end, and meanscontrolled by said last named means for regulating the rate at whichfuel is supplied to said pulverizer.

8.. In an air-swept conduit system including a pulverizer, wherein aportion of the mixture of pulverized material and carrier air dischargedfrom the pulverizer is withdrawn from said system and a remainingportion of said mixture is returned to said system for recycling throughsaid pulverizer, the method of controlling the operation of saidpulverizer at varying capacities which comprises feeding material to bepulverized to said pulverizer, supplying carrier air to said pulverizer,each from a source outside said system, measuring in terms ofdifferential pressure the rate at which carrier air is supplied to saidpulverizer, measuring in terms of differential pressure the rate offluid flow through said .pulverizer, measuring in terms of differentialpressure the rate at which pulverized material and carrier air arereturned to the pulverizer, and regulating the rate at which material tobe pulverized is fed to the pulverizer in accordance with the resultingthree measures of differential pressure.

9. In a system of the class described, an airswept pulverizer arrangedto discharge a fluent mixture of pulverized fuel suspended in air, meansfor supplying fuel to said pulverizer, means for returning a portion ofsaid mixture to said pulverizer and for mingling said portion with airsupplied to said pulverizer, means for measuring the rate of air flow tothe pulverizer, means for measuring the differential pressure across apredetermined portion of said pulverizer, means for measuring the rateat Which said portion of the mixture is returned to the pulverizer, andmeans conjointly responsive to said three named measuring meansforregulation the rate at which fuel is supplied to saidpulverizer.

10. In combination with an air-swept pulverizer arranged to discharge afluent mixture of pulverized material suspended in a stream of carrierair, means for supplying material to be pulverized to said pulverizer,means for returning a mixture of pulverized material and air to saidpulverizer at a rate less than the rate at which said initial mixture ofpulverizable material and carrier air is discharged from the pulverizer,means for measuring the rate of flow of carrier air to said pulverizer,means for measuring the difierential pressure across a predeterminedportion of said pulverizer, means for measuring the rate at which saidpulverized material and air are returned to the pulverizer, and meansunder thejoint control of said three named measuring means forregulating the rate at which said material to be pulverized is suppliedto said pulvermen 11. In combination with a pulverizer having a grindingzone in a lower portion thereof comprise ing an annular grinding surfacetogether with a circular row of reliable grinding elements cooperatingwith said surface, means for feeding material to be pulverized to saidgrinding zone from above, mean forming an annular throat passagemarginally of said grinding surface for admitting air into proximitywith said grinding zone from below, means for maintaining an upwardcurrent of air through said throat passage for discharging from saidpulverizer a fluent mixture comprising pulverized material suspended insaid air, a main conduit having its opposite ends open to the interiorof said pulverizer above and below said annular throat passage, saidconduit forming with said pulverizer a closed circulating path for aportion of the total mixture initially discharged from said pulverizer,means for regulating the rate at which said material is fed to saidgrinding zone comprising means responsive to therate of air delivery tosaid annular throat passage relative to the rate of fluid flow through apredetermined portion of said pulverizer inclusive of said annularthroat passage, and means for rendering said regulating means operativein accordance with the rate at which said portion of said output mixtureis re turned to said pulverizer.

12. In combination with a pulverizer having a grinding zone in a lowerportion thereof wherein a reserve of material in the process ofpulverization is maintained during normal operation, said grinding zonebeing defined by upper and lower grinding rings and a circular series ofmetal balls operating therebetween, means for feeding material to bepulverized to said pulverizer above said grinding zone, means forming anannular throat passage interiorly of said lower ring for admitting airto said grinding zone from below. means for maintaining an upwardcurrent of air through said throat passage and grinding zone fordischarging from said pulverizer a fluent mixture comprising pulverizedmaterial suspended in said air, a main conduit having its opposite endsopen to the interior of said pulverizer at the upper and lower sides ofaid grinding zone, said conduit forming with said pulverizer a closedcirculating path for at least a portion of the total mixture initiallydischarged from said pulverizer, means for measuring in term ofdifferential pressure the rate at which air is delivered to said throatpassage, means for measuring in terms of difierential pressure the rateof fluid flow through a predetermined portion of said pulverizerincluding said throat passage and said grinding zone, means formeasuring in term of differential pressure the rate of flow of theportion of said mixture being returned to said pulverizer, and meansrendered operative in response to said three named measuring meansacting jointly for controlling the rate at which material to bepulverized is fed to said pulverizer.

JAMES L. HARVEY.

